Organopolysiloxane compositions which can be vulcanized at temperatures of from 200.degree. to 400.degree. C. at substantially atmospheric pressure to form a tack free surface without bubbling are described in U.S. Pat. No. 2,723,966 to Youngs. The organopolysiloxane compositions described in the above patent consist of organopolysiloxanes containing methylpolysiloxanes in which up to 30 mol percent of the organopolysiloxanes consist of a copolymerized siloxane of phenylmethylsiloxane, diphenylsiloxane, methylvinylsiloxane and phenylvinylsiloxane, a filler and a dichlorobenzoyl peroxide containing two chlorine atoms per benzoyl radical. Japanese Patent Application 60-120,755 (published June 28, 1985, M. Fukushima, Shin-Etsu Chemical Co.) and Japanese Patent Application JP-A 60-120,754 (published June 28, 1985, K. Numata, Shin-Etsu Chemical Co.) describe heat-vulcanizable silicone rubber compositions which contain, in addition to the organopolysiloxane to be vulcanized and an organic peroxide, at least one polysilane, polysilalkylenesiloxane and/or polyphenylenesiloxane, in which each have at least two Si-H groups per molecule.
Therefore, it is an object of the present invention to provide organopolysiloxane compositions which vulcanize at elevated temperatures without liberating toxic polyhalogenated aromatic compounds during or after vulcanization and which are substantially free of discoloration. Another object of the present invention is to provide organopolysiloxanes which vulcanize at elevated temperatures that do no contain toxic polyhalogenated aromatic compounds. A further object of the present invention is to provide heat vulcanizable organopolysiloxane compositions which are substantially free of hydrolysissensitive Si-H groups.